Rating:
# UMassCTF 2022 writeup - quickmaths
- Write-Up Author: [Ivan Mak](https://ank.pw/tech/)
Flag : UMASS{s3v3naten1n3}
## Question:
Connect to [34.148.103.218:1228](34.148.103.218:1228)，solve 1000 of math problems
## Write up
### 1. use netcat
```shell
nc 34.148.103.218 1228
```
```shell
You must solve 1000 of these math problems that are outputted in the following format {number} {operation} {number} to get the flag.
Division is integer division using the // operator.
The input is being checked through python input() function.
Good luck!
-21 // 95
-1
Correct!
-52 - 53
-105
Correct!
-28 // 65
```
There are some maths need to solve. Actually, It can be solved manually. but this is not an effective idea.
### 2. use pwntools
[Pwntools](https://docs.pwntools.com/en/stable/) is a great tools to solve the remote program automatically via python.
```python
from pwn import *
p = remote("34.148.103.218",1228)
p.recvuntil("Good luck")
p.recvline()
p.recvline()
for i in range(1000):
print("======",i)
a = p.recvline()
a = a.decode('ascii').strip()
print("Q",a)
b = eval(a)
print("A:",b)
p.sendline(str(b))
p.recvuntil("Correct!")
p.recvline()
c = p.recvline()
print(c)
```
But there is a tricky problem, process always be interrupted due to `EOFError` issue.
It is due to server side has no response, pwntools will be interrupted.
### 3. keep connection alive at server side
Modify the code, use while-loop instead of for-loop. Make pwntools to keep connection alive at the server side when server side has no response.
```python
from pwn import *
p = remote("34.148.103.218",1228)
p.recvuntil("Good luck")
p.recvline()
p.recvline()
i = 1
while i <= 1000:
try:
print("======",i)
a = p.recvline()
a = a.decode('ascii').strip()
print("Q",a)
b = eval(a)
print("A:",b)
p.sendline(str(b))
p.recvuntil("Correct!")
p.recvline()
i +=1
except:
p = remote("34.148.103.218",1228)
c = p.recvline()
print(c)
```
